The long term goal of this study is a molecular analysis of mechanisms underlying gene regulation and pattern formation during early development. In Drosophila melanogaster, ectodermal differentiation into neural vs. epidermal tissue appears to be regulated by a small class of interacting genes, collectively termed the neurogenic loci. The best described neurogenic locus, Notch, appears to encode a complex transcription unit. The multiple RNA products of Notch will be analyzed through cDNA cloning and DNA sequencing. Specific classes of transcript will be localized during early development via in situ hybridization of radioactive probes to tissue sections. Notch-encoded polypeptides will be investigated using hybridization selection and in vitro translation. A second neurogenic locus, big brain or mastermind, will be cloned and characterized at the molecular level. The strategies for cloning include transposon tagging with P elements through hybrid dysgenesis, chromosomal walking, and microdissection of polytene chromosomes. Determination of the physical limits of the locus will involve analyses of chromosomal rearrangements and DNA transformation assays. The physical structure and transcriptional activity of the locus will be studied by Northern blotting, cDNA characterization, S1 nuclease protection, and primer extension. Cloned sequences will be utilized as probes to investigate interactions of big brain or mastermind with other neurogenic loci.